1270                                                PRACTICE FINAL EXAM                                                       

 

 

1.      (75 points)

 

                 

 

 

         Design an electronic thermometer using the circuit diagram shown above. The voltage v3 is used to indicate temperature. Use a thermistor with a resistance described by

 

                                                 

 

         where Ro = 12 kΩ and T is temperature in °K.

 

         a.      Choose circuit components that will produce the following:

 

                                          v3 = 0 V            when            T = 273°K

                                          v3 = 1 V            when            T = 373°K.

 

                  Be sure the operational amplifier would not saturate. Explain your work carefully.

 

         b.      Using the component values you chose above, calculate v3 when T = 323°K. Make a rough sketch of v3 vs. T on the basis of the values when T = 273°K, 323°K, and 373°K. On the same axes, sketch the ideal linear response. Comment on the quality of the response compared to the desired linear response.

 

2.      (70 points)

 

 

 

         After having been c for a long time, the switch is moved to position d at t = to.

 

 

                                         

 

 

         a.   Choose either an R or C to go in box a and either an R or C to go in box b to produce the vo(t) shown in the diagram. Specify which element goes in each box, and specify each value.

 

         b.   Sketch v2(t), the voltage across the circuit element in box b. Show numerical values appropriately.

 

         c.   Sketch v1(t), showing numerical values appropriately.

 

         d.   Sketch v4(t). Show numerical values for t < to, for to < t < (to + 2 ms), and for t > (to + 2 ms). Use the ideal model of the diode: when forward biased, its resistance is zero; when reversed biased, its resistance is infinite.

 

         Explain your work carefully.

3.   (30 points)

 

                     

 

      a.   Choose the value of ZL that will absorb maximum average power.

      b.   Calculate the value of that maximum average power absorbed by ZL.

 

4.      (25 points)

                                

 

         a.      Write an equation for the node voltages v1, v2, and v3 in the form:

                                                   g11v1 + g₁2v2 + g13v3 = i1

                                                   g21v1 + g22v2 + g23v3 = i2

                                                   g31v1 + g32v2 + g33v3 = i3

                  List the numerical values of gij's and ij's.